At present, operation of devices engageable with loose abrasive materials, such as sizing screens, conveyers, and ore processing machines, poses a major problem for extending the service life and reducing the wear of surfaces subjected to vigorous action of loose abrasive materials.
Elements from elastomers (such as rubber or polyurethane) used for such purposes are characterized by low resistance to wear and short service life. This is due to the fact that in most such devices the elastomeric elements forming the surface engageable with loose abrasive materials are normally mounted with a tension or strain resulting in fast wear of their working surfaces, low resistance to rupture, and tendency of crack formation.
There is known a sifting element of a screening surface (cf., Catalogue of the swedish company "Trelleborg", pp. 21 and 27) comprising a base with a plurality of through holes made up of two or more layers of elastomer having different mechanical characteristics, or made of a single layer and reinforced with a cord element or special metal inserts. The top layer forming the working surface of the element is fabricated from a soft wear-resistant rubber, whereas the other successive layers are made of a more rigid rubber or polyurethane.
There are also known grading screens "Duenero", "DUO", "Trelleborg", "Treliflex" (cf., Catalogue of the swedish company "Trelleborg", pp. 21 and 27) with frames thereof accommodating a plurality of the aforedescribed sifting elements. Such screens are very resistant to wear, but have a rather intricate structural arrangement of these elements.
There is known an elastic sifting element of a sizing screen (cf., SU, A, 1,039,587) comprising a flat base with a plurality of holes and stiffening ribs, and a sizing screen including a frame having secured thereto a plurality of said elastic sifting elements. The elastic sifting elements are secured with a tension on the frame of the screen to form a working surface subjected to intensive wear during engagement with loose abrasive materials which reduces the service life of the sizing screen.
In addition, stretching of the elastic sifting elements cause deformation and change in the size of the holes, as well as an increase in the clearances between the adjacent elastic sifting elements to a magnitude exceeding the maximum allowable grading size, which reduces the efficiency of screening.
There is also known an elastomeric element for forming surfaces engageable with loose abrasive materials (cf., SU, A, 1,080,885) comprising a base having a working surface engageable with loose abrasive materials, and at least two attachment means connected to the base. The base of the element is fashioned as a flat belt having wedge-shaped recesses spaced equidistantly along one edge. The two attachment elements are provided at the ends of the base for the base to be mounted with tension in the frame of the sizing screen.
There is further known a sizing screen for grading loose abrasive materials according to size (cf., SU, A 1,080,885) comprising a frame having secured thereon a plurality of sifting elements forming a surface engageable with loose abrasive materials. The surface of the sizing screen engageable with the loose abrasive materials is formed from the above elements secured in the frame of the screen so that the edge with projections of the preceding belt adjoins the straight edge of the succeding belt to form holes for the passage of the fine fraction of the loose abrasive materials.
The sifting elements are mounted in the frame of the sieve with a relative tension of 25-30%. As is known, for elastomers in such a strained state, the wear due to engagement with loose abrasive materials is almost doubled. Therefore, screens made up of such known elastomeric elements have a rather short service life.